High-volume fabrication of semiconductors will reach a critical demand in the next few years. Throughput of wafer processing, and in particular, the costs associated with the development of each workpiece are critical for the survival of each semiconductor manufacturer. Additionally, because the price the end users are willing to pay for the semiconductors which are constantly being reduced, the cost associated with each wafer must be reduced as production increases.
Typically, the horizontal stack furnace, as shown as prior art FIG. 1A, has served reasonably well in the thermal processing of wafers. In the horizontal stack furnace, wafers are thermally processed by various methods, including lamps, resistance heated coils, and other methods. Horizontal stack ovens are problematic in that they require more mechanical or manual loading and unloading movements, each of which may result in contamination or the loss of an entire wafer boat. Furthermore, uniform thermal distribution is more difficult in the horizontal stack oven than in other oven configurations. The horizontal stack oven also has resulted in poor environmental control of the wafer environment.
A solution for poor environmental control of the horizontal stack has been the use of the vertical processing furnace as shown in prior art FIG. 1B (ASM), which allows for the improved processing of wafers with regard to contamination. However, vertical processing has a particularly problematic limitation in that the wafers must be supported to maintain a perfect wafer shape.
In the future, all tools may require full automation as well as full SMIF and FOUP compatibility. All tools should integrate the factory host automation system. Additionally, the market shift from 200 mm to 300 mm wafers will require retooling. However, in some sectors certain applications remain more economical at 200 mm.
The currently installed base of horizontal furnaces will be gradually phased out and replaced with automated furnaces. For economic reasons, fabrication labs will take advantage of the benefits of each type of the processing tool on an application-specific basis. Instead of using just one type of furnace, regardless of the application, furnaces will be matched to the processes for which they are most suited. For example, mini-batch furnaces might be used for exotic chemical vapor deposition processes and vertical furnaces will be used for all generic LPCVD processes.
Not all device technology demands particle control or processing that is provided by the expensive vertical furnace. Therefore, not all wafer processing justifies the cost of vertical furnace. For example, smaller chips, such as transistors, thyristors and side-actors will use large line widths and single wafer tools will be used for rapid thermal process.
However, continuing the diffusion processes with the traditional horizontal stack furnaces is not feasible; this is because the support and development of these furnaces is subsiding. When wafer circuit geometries shrink or reliability issues become a serious cost factor, options are limited for wafer processors. In-line horizontal furnaces cannot be the system of choice for future fabs because they are difficult to fully automate and increases the investment to support existing horizontal furnaces. It is also clear that the vertical furnaces are not always a viable economic option leaving a large gap in the market. Horizontal furnaces have the advantage that wafers are processed “on edge” standing vertically, whereas the vertical furnace operates with the wafers lying horizontally, limiting the throughput and higher temperature capabilities.
Some of these problems have been partially addressed in U.S. Pat. Nos. 6,281,479 and 6,291,801 to Guidotti, and currently assigned to International Business Machines of Armonk, N.Y., which are hereby incorporated by reference. The Guidoitti disclosures teach a workpiece processing system in which the thermal processing is performed in a semicircular toroidal oven and which is shown in prior art FIG. 2. While the Guidotti teachings offer some advantage over the conventional fabrication ovens which provides a somewhat reduced footprint, they fail to provide advantages of increased throughput and future automation requirements.